Preamplifier for ADF loop antenna

Abstract

An antenna and preamplifier system suitable for use with airborne ADF equipment. Each of two orthogonally oriented loop antennas feed a different one of two preamplifiers. Each preamplifier includes an impedance establishing network and a pair of negative feedback amplifiers operating in push-pull.

What is claimed is: 
     
       1. For use with an automatic direction finder, an antenna and preamplifier system comprising: (i) two loop antenna windings,   (ii) two substantially matched gain preamplifiers, each being associated with a different one of said antenna windings, each preamplifier comprising: (a) an input impedance establishing network having input means connected for receiving excitation from opposite ends of the preamplifier-associated antenna winding,   (b) a pair of negative feedback amplifiers for operating in push-pull relationship and having input means connected for receiving excitation from opposite ends of the preamplifier-associated antenna winding, and   (c) an output receiving means having input means connected for receiving excitation from the negative feedback amplifier pair.     
     
     
       2. A system as defined in claim 1 wherein said output receiving means comprises a transformer having a primary winding connected for receiving excitation from said negative feedback amplifier pair. 
     
     
       3. A system as defined in claim 2 wherein the input impedance network includes resistance of predetermined value. 
     
     
       4. A system as defined in claim 3 wherein said transformer has a first secondary winding, and wherein said input impedance network comprises said resistance of predetermined value and said first secondary winding connected in series. 
     
     
       5. A system as defined in claim 2 wherein each negative feedback amplifier comprises (i) an amplifier with high open loop voltage gain and (ii) means for providing feedback to said amplifier in an amount sufficient for establishing the voltage gain of the negative feedback amplifier. 
     
     
       6. A system as defined in claim 5 wherein said feedback providing means comprises a network of resistors. 
     
     
       7. A system as defined in claim 6 wherein said resistors are precision resistors. 
     
     
       8. A system as defined in claim 5 wherein said transformer further includes one or more secondary windings additional to said first secondary winding, and wherein said feedback providing means comprises one or more of said additional secondary windings. 
     
     
       9. A system as defined in claim 5 wherein said amplifier with high open loop voltage gain includes a FET transistor connected for receiving, at its gate electrode, excitation from the antenna winding, and further connected for receiving, at its source electrode, feedback derived from amplifier output. 
     
     
       10. A system as defined in claim 5 wherein said amplifier with high open loop voltage gain comprises at least two cascaded amplification stages. 
     
     
       11. A system as defined in claim 10 wherein the first stage comprises a FET transistor. 
     
     
       12. A system as defined in claim 11 wherein said FET transistor is connected for receiving, at its gate electrode, excitation from the antenna winding. 
     
     
       13. A system as defined in claim 12 wherein the second stage comprises a bipolar transistor. 
     
     
       14. A system as defined in claim 12 wherein said feedback providing means comprises a resistive network connected for providing feedback to the source electrode of said FET transistor. 
     
     
       15. A system as defined in claim 12 wherein said transformer further includes one or more secondary windings additional to said first secondary winding, and wherein said feedback providing means comprises one or more of said additional windings connected for supplying feedback to a predetermined one, or both, of the gate electrode and the source electrode, of the FET transistor.